1. Field of the Invention
The present invention relates to a ring configuring method and a node apparatus used in the ring, and, in particular, to a ring configuring method and a node apparatus used in the ring in which protection according to a manner of a bidirectional line switched ring can be performed by an open-ring configuration.
2. Description of the Related Art
Recently, a bidirectional line switched ring (BLSR) is mainly used as a configuration of a network of optical transmission apparatuses.
By a BLSR, one time slot in a line is used by a plurality of paths, and another time slot is possessed as a spare in common by the plurality of paths, and, thereby, high line holding efficiency can be achieved.
Further, as a line comes to have a large capacity, a large-scale configuration such that a distance between optical transmission apparatuses is several hundreds of kilometers is achieved.
However, when a network is constructed, there is a case where, from the view points of costs of setting and operating optical transmission apparatuses and so forth, all the apparatuses are not set so as to form a ring at once, but the number of optical transmission apparatuses is increased gradually, thus the network is enlarged, and, finally, a BLSR is formed thereof and is operated.
For example, as shown in FIG. 1, nodes (optical transmission apparatuses) A and B are connected by optical fibers, and, then, nodes B and C are connected by optical fibers. Thus, a linear configuration (that is, an open-ring configuration) is formed.
Then, when a node D is added, as shown in FIG. 2, the node D is connected to the nodes A and C by optical fibers, respectively. Thus, a ring configuration is formed. Then, a switching protocol is changed from a linear switching protocol into a BLSR switching protocol.
In a linear configuration, only span switching using a short path between nodes between which a fault occurs is available. In contrast to this, in a ring configuration, not only span switching using a short path between nodes between which a fault occurs but also ring switching using a long path are available.
Accordingly, in order to enable the BLSR switching protocol to properly function, it is necessary to construct a topology table and squelch tables for each node (as disclosed in Japanese Laid-Open Patent Application No. 9-93278, xe2x80x98Ring Transmission System and Squelch Method for the Systemxe2x80x99, filed by the present applicant).
A topology table holds topology which is node connection information indicating an arrangement of nodes forming a ring. A squelch table holds a fault condition such as to disconnect each path so as to prevent a signal in the erroneous path from being output due to BLSR switching at a time of a occurrence of a fault.
A squelch table is set for each path based on a topology table. Accordingly, when the number of paths passing through a single optical fiber is as large as tens through hundreds, it is very difficult to set the squelch tables at once accurately.
In the related art, there is an art of automatically constructing a topology table and squelch tables for a ring configuration. However, it is not possible to apply this art to a linear configuration, and to automatically construct a topology table and squelch tables.
Further, k1 and k2 bytes of a line overhead of a main signal of a SONET (Synchronous Optical NETwork) are used in common by a linear switching protocol and a BLSR switching protocol. However, methods of using the respective bytes are different.
Accordingly, when switching is performed due to an occurrence of a fault in the middle of a change of a switching protocol from a linear switching protocol to a BLSR switching protocol, an erroneous operation is performed for dealing with (or relieving from) the fault. In order to prevent such an erroneous operation from being performed, it is necessary to stop both switching protocols when a switching protocol is changed.
As it is necessary to construct a topology table and squelch tables for each node during the stopping of the switching protocols, it is not possible to perform the change of switching protocol smoothly within a short time.
The present invention has been devised in consideration of the above-described problems, and an object of the present invention is to provide a ring configuration method and a node apparatus used the ring in which it is possible to construct topology necessary for a BLSR configuration in an open-ring configuration, and, to perform switching by a BLSR switching protocol in the open-ring configuration.
A ring configuring method of configuring a network in which a plurality of nodes are connected linearly, and performing topology construction for the ring by circulating topology data through the respective nodes and collecting connection information of the respective nodes, according to the present invention, comprises the steps of:
a) providing in the topology data a flag indicating whether the connection information is collected in each node;
b) inverting the flag at a terminal station which is an end node of the open ring, and turning the topology data there;
c) causing the topology data to pass through a node other than any terminal station as it is; and
d) adding the connection information to the topology data in each node according to the flag, and performing topology construction.
Through the steps of b), c) and d), it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR, and, based thereon, to construct squelch tables.
The method may further comprises the steps of:
e) sending the topology data in any direction from any node, and circulating the topology data in the ring; and
f) receiving the topology data by the node in a direction opposite to that of the step e), and performing topology construction.
Through the steps of e) and f), it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR.
The method may further comprise the steps of:
e) sending the topology data in both directions from any node, and circulating the topology data in the ring; and
f) configuring the topology when the topology data received by the node in directions opposite to those of the step e), respectively, coincides.
Through the steps of e) and f), it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR.
A node apparatus of a network in a configuration of a ring in which a plurality of nodes are connected linearly, according to the present invention, comprises:
a collecting/passing control part receiving topology data circulating the ring, and transmitting the topology data after adding an own node ID when a flag provided in the topology data indicates to collect connection information, but causing the topology data to pass through the own apparatus when the flag indicates not to collect the connection information; and
a turning/passing control part turning the topology data after inverting the flag in a case where the own apparatus is a terminal station which is an end node of the open ring, but causing the topology data to pass through the own apparatus leaving the flag as it is in a case where the own apparatus is not any terminal station.
Through turning the topology data after inverting the flag in a case where the own apparatus is a terminal station which is an end node of the open ring, but causing the topology data to pass through the own apparatus leaving the flag as it is in a case where the own apparatus is not any terminal station, and performing topology construction in each node according to the flag, it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR, and, based thereon, to construct squelch tables.
The node apparatus may further comprise a one-direction transmitting part transmitting the topology data in one direction, and circulating the topology data in the ring, and
receiving the topology data in a direction opposite to the one direction, and performing topology construction.
Thereby, it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR.
The node apparatus may further comprise:
a both-direction transmitting part transmitting the topology data in both directions, and circulating the topology data in the ring; and a comparing part comparing the topology data received in directions opposite to the both directions, respectively, and
performing topology construction when a result of comparison of the comparing part is a coincidence.
Thereby, it is possible to automatically perform topology construction, in an open ring, necessary for a BLSR.
The node apparatus may further comprise a lockout-work ring part stopping ring switching of a manner of a bidirectional line switched ring when a ring fault occurs such that neither a work line nor a protection line connected to either side of the own apparatus can be used.
Thereby, it is possible to perform switching according to a BLSR switching protocol in an open ring, and, at this time, to prevent unnecessary line disconnection from occurring.
The node apparatus may further comprise:
a fixed-value setting part setting a fixed value to the flag when the own apparatus is set as a master; and
a changing part comparing the node ID of the own apparatus with the top node ID of the received topology data when the own apparatus is set as a master, and changing the own apparatus to a slave when the own apparatus cannot become the top of the topology data.
Thereby, even when a plurality of node apparatuses are set as masters, it is possible to reduce the masters so that a single node apparatus is a master, and, thereby, to perform topology construction so as to obtain single topology data.
The node apparatus may make setting as to whether the own apparatus is a master or a slave independently in a part transmitting the topology data in one direction and circulating the topology data in the ring and another part transmitting the topology data in the other direction and circulating the topology data in the ring.
Thereby, it is possible to set topology data individually for the part performing circulation in one direction and the other part performing circulation in the other direction, and, thereby, to improve the degree of freedom in setting topology data.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.